[AHW32-P12] Distribution of phosphate oxygen isotope in boring core samples for evaluation of phosphorus cycling in groundwater
Phosphorus (P) input through groundwater discharge plays a significant role in nutrient cycling and primary productivity in the coastal area (Slomp & Cappellen., 2004). Therefore, its biogeochemical cycling in underground environment is important in proper land management and understanding of natural systems. Recently, phosphate oxygen isotope ratio (δ18OPO4) has been used as a promising tool to elucidate the P cycling. Previous studies showed the possibility to evaluate P sources, metabolism by organism in some ecosystems (Paytan & McLaughlin 2011). However, it is not clear whether δ18OPO4 is useful for evaluating the P cycling of in underground environment, because few researches have applied the δ18OPO4 analysis for underground P cycling.
In the present study, we investigated the δ18OPO4 values of boring core samples and groundwater to clarify P cycling in underground.
A boring core (28 m depth) and groundwater (5 m and 28 m depth) were collected at The University of Shiga Prefecture, which is located on coastal area of Lake Biwa, central Japan. Boring core was divided by 1 m and ground to powder using a multi-bead shocker (Yasui Kikai) with tungsten carbide beads. The powdered boring core samples were immersed in 1 M HCl for 16 h to extract the inorganic P. Groundwater samples were filtered through 0.45-μm membrane filters (Advantec). The SRP concentration of each samples was measured using the molybdenum-blue method on a microplate spectrophotometer (Multiskan GO; Thermo Fisher Scientific). For the δ18OPO4 analysis, the extract and groundwater samples were converted to Ag3PO4 according to McLaughlin et al. (2004) or Tamburini et al. (2010). The δ18OPO4 values reported relative to the Vienna Standard Mean Ocean Water (VSMOW) of the Ag3PO4 samples were measured using a TC/EA-IRMS (thermal conversion elemental analyzer connected to a Delta plus XP via ConFlo III, Thermo Fisher Scientific) at the Research Institute for Humanity and Nature (RIHN).
The soluble reactive P (SRP) concentrations in 5 m and 28 m depth of groundwater were 0.74 and 6.78 μmol L-1, respectively. Deeper groundwater has much higher SRP concentration than river and lake water (< 0.7 μmol L-1) near The University of Shiga Prefecture. The δ18OPO4 values in 5 m and 28 m depth of groundwater were 15.1 and 17.1‰, respectively. In our poster, we will show the result of distribution of δ18OPO4 in boring core samples and discuss the P cycling in groundwater.
Reference
McLaughlin, K., Silva, S., Kendall, C., Stuart-Williams, H., and Paytan, A. (2004) A Precise Method for the Analysis of δ18O of Dissolved Inorganic Phosphate in Seawater. Limnolgy and Oceanography: Methods, 2, pp. 202−212.
Paytan, A., and McLaughlin, K. (2011) Tracing the sources and biogeochemical cycling of phosphorus in aquatic systems using isotopes of oxygen in phosphate. In M. Baskaran, ed. Handbook of Environmental Isotope Geochemistry. Berlin: Springer-Verlag, pp. 419–436.
Slomp, CP., and Cappellen, PV. (2004) Nutrient inputs to the coastal ocean through submarine groundwater discharge: Controls and potential impact. Journal of Hydrology, 295, pp. 64-86.
Tamburini, F., Bernasconi, SM., Angert, A., Weiner, T., and Frossard, E. (2010) A Method for the Analysis of the δ18O of Inorganic Phosphate Extracted from Soils with HCl. European Journal of Soil Science, 61, pp. 1025–1032.
In the present study, we investigated the δ18OPO4 values of boring core samples and groundwater to clarify P cycling in underground.
A boring core (28 m depth) and groundwater (5 m and 28 m depth) were collected at The University of Shiga Prefecture, which is located on coastal area of Lake Biwa, central Japan. Boring core was divided by 1 m and ground to powder using a multi-bead shocker (Yasui Kikai) with tungsten carbide beads. The powdered boring core samples were immersed in 1 M HCl for 16 h to extract the inorganic P. Groundwater samples were filtered through 0.45-μm membrane filters (Advantec). The SRP concentration of each samples was measured using the molybdenum-blue method on a microplate spectrophotometer (Multiskan GO; Thermo Fisher Scientific). For the δ18OPO4 analysis, the extract and groundwater samples were converted to Ag3PO4 according to McLaughlin et al. (2004) or Tamburini et al. (2010). The δ18OPO4 values reported relative to the Vienna Standard Mean Ocean Water (VSMOW) of the Ag3PO4 samples were measured using a TC/EA-IRMS (thermal conversion elemental analyzer connected to a Delta plus XP via ConFlo III, Thermo Fisher Scientific) at the Research Institute for Humanity and Nature (RIHN).
The soluble reactive P (SRP) concentrations in 5 m and 28 m depth of groundwater were 0.74 and 6.78 μmol L-1, respectively. Deeper groundwater has much higher SRP concentration than river and lake water (< 0.7 μmol L-1) near The University of Shiga Prefecture. The δ18OPO4 values in 5 m and 28 m depth of groundwater were 15.1 and 17.1‰, respectively. In our poster, we will show the result of distribution of δ18OPO4 in boring core samples and discuss the P cycling in groundwater.
Reference
McLaughlin, K., Silva, S., Kendall, C., Stuart-Williams, H., and Paytan, A. (2004) A Precise Method for the Analysis of δ18O of Dissolved Inorganic Phosphate in Seawater. Limnolgy and Oceanography: Methods, 2, pp. 202−212.
Paytan, A., and McLaughlin, K. (2011) Tracing the sources and biogeochemical cycling of phosphorus in aquatic systems using isotopes of oxygen in phosphate. In M. Baskaran, ed. Handbook of Environmental Isotope Geochemistry. Berlin: Springer-Verlag, pp. 419–436.
Slomp, CP., and Cappellen, PV. (2004) Nutrient inputs to the coastal ocean through submarine groundwater discharge: Controls and potential impact. Journal of Hydrology, 295, pp. 64-86.
Tamburini, F., Bernasconi, SM., Angert, A., Weiner, T., and Frossard, E. (2010) A Method for the Analysis of the δ18O of Inorganic Phosphate Extracted from Soils with HCl. European Journal of Soil Science, 61, pp. 1025–1032.